• MESO: Mesoscale Discussion 0453

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Apr 28 19:43:02 2021
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    ACUS11 KWNS 281942
    SPC MCD 281942=20

    Mesoscale Discussion 0453
    NWS Storm Prediction Center Norman OK
    0242 PM CDT Wed Apr 28 2021

    Areas affected...Portions of south-central TX

    Concerning...Severe potential...Watch likely=20

    Valid 281942Z - 282145Z

    Probability of Watch Issuance...95 percent

    SUMMARY...Severe thunderstorms capable of producing very large hail,
    damaging wind gusts, and perhaps a few tornadoes are expected to
    develop this afternoon. Watch issuance will likely be needed.

    DISCUSSION...Persistent low-level east-southeasterly upslope flow is
    occurring this afternoon across south-central TX. This will support
    convective initiation across the higher terrain of northern Mexico
    adjacent to Del Rio TX. In fact, several attempts have recently
    occurred along the Rio Grande River in Val Verde County, and a
    lightning flash has been observed with developing convection in
    adjacent northern Mexico. Rich low-level moisture, characterized by
    upper 60s to low 70s surface dewpoints, is in place across this
    region. This moisture coupled with strong diurnal heating and
    steepening mid-level lapse rates is supporting MLCAPE of 1500-2500
    J/kg east of a surface dryline.

    Enhanced mid-level flow associated with an upper low over the
    Southwest and northern Mexico will remain over this region through
    the afternoon and evening. Related strong effective bulk shear of
    50-60+ kt and long, straight hodographs above the boundary layer
    will support supercells, with some potential for storm splits. Very
    large hail of 2 to 3+ inches appears likely with these initially
    discrete storms given the rather favorable thermodynamic and
    kinematic environment. As additional storms form through the late
    afternoon and into early evening, severe wind gusts may also occur
    given the presence of steep low-level lapse rates where strong
    diurnal heating has occurred. Although low-level winds across
    south-central TX are not forecast to be very strong, there will be
    ample directional shear/veering of the wind profile though the
    boundary layer. This should support low-level rotation with any
    supercells that can form, and isolated tornadoes appear possible.
    Watch issuance will likely be needed to address this anticipated
    severe threat.

    ..Gleason/Hart.. 04/28/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!tPSQEEJjsiLNHQRpojd3xDkcjXnfVWBzJZovAxsvRI4C7r_4PoDzxyIV2sz0SFA5ydFP3NYe$=
    for graphic product...


    LAT...LON 29730153 30150129 30420067 30599987 30719900 30719844
    30429823 29959841 29229917 28569999 28570048 29010072
    29300099 29730153=20

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